(1) Field of the Invention
The present invention relates to a process for the preparation of monodisperse polymer particles having an increased particle size. More particularly, the present invention relates to a process in which the solubility of a monomer present in a dispersion medium of seed polymer particles is reduced to make the monomer absorbed in the seed polymer particles and polymerization is carried out in this state, whereby polymer particles having an increased particle size are prepared.
(2) Description of the Related Art
The emulsion polymerization process, the suspension polymerization process and the dispersion polymerization process are known as the process for the preparation of spherical polymer particles. Each of these processes is characterized by the particle size, particle size distribution and molecular weight of the obtained polymer. In the emulsion polymerization process, monodisperse fine particles of a high polymer can be obtained, but only particles having a particle size smaller than 1.0 .mu.m are obtained. In contrast, in the suspension polymerization process, particles having a particle size larger than 10 .mu.m can be obtained, but a product other than a product having a polydisperse particle size distribution cannot be synthesized. In connection with the dispersion polymerization, the synthesis of monodisperse particles having a particle size of about 7 .mu.m has been reported, but it is impossible to control the molecular weight of the polymer constituting the particles and the particle size, and kinds of monomers that can be used are limited.
As the means for overcoming these defects, there has been proposed the so-called two-staged swelling process in which monodisperse particles synthesized by the emulsion polymerization are swollen by an oligomer or solvent and then swollen by a monomer and then, polymerization is carried out, as disclosed in Journal of Polymer Science, Polymer Symposium, 72, 225-240, (1985).
This known process, however, is defective in that the complicated means, that is, the two-staged swelling, is necessary, a long time is required for the swelling operation, and the productivity is low.
If spherical polymer particles having a particle size of several .mu.m to scores of .mu.m and a monodisperse particle size distribution are obtained, since the particle size distribution is sharp and such an operation as classification is not necessary, it is expected that they will be used as electrophotographic toners, gap-adjusting agents for liquid crystal display panels, standard particles of a Coulter counter, column fillers for the chromatography or the like, carriers for immune diagnosis agents, cosmetic fillers and the like.